The present invention relates to a device for determining the position of a structure on an object. In particular, the invention relates to a device for determining the position of a structure on an object in relation to a coordinate system. The object is placed on a measuring table which is movable in one plane, wherein a block defines a plane in which the measuring table is movable. At least one laser interferometer for determining a positional displacement of the measuring table in the plane is further provided. At least one optical arrangement is provided for transmitted light illumination and/or reflected light illumination.
The invention further relates to the use of at least one illumination apparatus with a device for determining the position of at least one structure on an object.
The invention further relates to the use of protective gas with a device for determining the position of at least one structure on an object.
A measuring device for measuring structures on masks or substrates used for the production of semiconductors is known from the lecture manuscript “Pattern Placement Metrology for Mask Making” by Dr. Carola Bläsing. The lecture was given on the occasion of the Semicon Education Program congress in Geneva on 31 Mar. 1998. This lecture manuscript discloses the basis of a device for determining the positions of structures on a substrate. With regard to the details of the operation and the structure of a device of this type, reference should be made to FIG. 1 of this patent application, which illustrates the prior art.
In measuring equipment and devices of the prior art, optical sensing methods are still favoured, although the measuring accuracy required (currently in the region of a few nanometers) lies far beneath the resolution achievable with the light wavelength used (the spectral region of the near UV). The advantage over devices that operate using optical measuring methods lies essentially in a less complex design and easier operation compared with systems using other sensing systems, for example, with X-rays or electron beams.
A measuring device for measuring structures on a transparent substrate is also disclosed by the published application DE 198 19 492. The measuring device comprises a reflected light illumination apparatus, an imaging device and a detector device for imaging the structures on the substrate. The substrate is placed on a displaceable measuring table which can be displaced perpendicularly to the optical axis. The position of the measuring table is determined by interferometric means. The detector apparatus registers the edge profiles created by the structures. Based on the profiles, the position of the edges of the respective structure can be determined in relation to a fixed coordinate system.
A device of this type is disclosed, for example, in DE 199 49 005, DE 198 58 428, DE 101 06 699 and DE 10 2004 023 739. In all these prior art documents, a coordinate measuring machine is described with which structures on a substrate can be measured. The substrate is placed on a measuring table which can be moved in the X-coordinate direction and in the Y-coordinate direction. Suitable light sources are used for illuminating the substrate. The substrate can be illuminated either by transmitted light and/or by reflected light. For imaging the illuminated structures, a measuring objective which is also arranged in the reflected light ray path is provided. The light collected by the objective lens is directed to a detector which, in conjunction with a computer, converts the received signals into digital values.
The structures on wafers or the masks used for exposure permit only extremely small tolerances. In order to check these structures, a very high degree of measuring accuracy (currently in the nanometer range) is needed. A method and a measuring device for determining the positions of these structures are disclosed in the German specification laid open to inspection DE 100 47 211 A1. For details of the positional determination described, reference is therefore expressly made to this document.
Previously, devices for measuring masks or structures on masks have used mercury-xenon lamps for illuminating the measuring optical system. These have a very marked intensity maximum in their spectrum at 365 nm. This wavelength or the region round this wavelength is used for illuminating the measuring optical system. The energy in this line has previously been sufficient for illuminating the measuring optical system. In future systems, due to the increased demands placed on the resolving power, it will be necessary to change over to ever shorter wavelengths (248 nm, 193 nm, 157 nm). This higher resolution will be demanded by customers since the structures on the masks are becoming ever smaller. However, at these wavelengths, the lamps typically used for illumination in microscopes do not produce any spectral lines of sufficient intensity. It is therefore necessary to make use of alternative light sources or alternative configurations of the device for measuring structures on a substrate. The necessary spectral lines are not present at sufficient intensity in the wavelength range required here.